1. Field of the Invention
The present invention relates to an integrated circuit apparatus, and more particularly to an integrated circuit apparatus provided with an oscillating circuit.
2. Description of the Prior Art
Some microcomputers have a time counting function. In such a microcomputer, it is required to activate an oscillating circuit provided therein to perform the time counting function and to display the time even while a central processing unit (CPU) is performing its original operations. In a microcomputer of a type not having the time counting function, a battery used as a power source normally lasts long since the power is hardly consumed when the CPU is in a disabled state. In a microcomputer of the type having the time counting function, however, the life of the battery is unavoidably shortened since an oscillating circuit provided therein is always activated. For this reason, it has been attempted to find a way to minimize the power consumption when the CPU is in the disabled state.
In a prior art shown in FIG. 1, an oscillating circuit 2 formed in a microcomputer 1 has a p-channel metal oxide semiconductor (MOS) transistor 4 and an n-channel MOS transistor 5 which are of CMOS (complementary metal oxide semiconductor) connection. The source of the p-channel MOS transistor 4 is connected through a resistor 6 to a power supply line 8 and the source of the n-channel MOS transistor 7 is connected through a resistor 5 to ground. With this connection, the electric current is limited by the resistors 6 and 7. As a result, power consumption is restrained. In FIG. 1, numeral 3 is an externally-attached quartz resonator, while numerals 9 and 10 are externally-attached capacitors. An oscillation output is transmitted through a line 11 to a predetermined circuit.
In an oscillating circuit using such a current limiting resistor, since power consumption reduction is limited, no satisfactory results are obtained. This is because the values of the resistors 6 and 7 can only be approximately 100k.OMEGA. since, if the values of the resistors 6 and 7 are increased, the starting characteristic of the oscillating circuit obtained when the power is turned on is deteriorated. If a resistor value is increased, the current which flows through the circuit will not sufficiently be small in a circuit having a high supply voltage.